By coincidence, I meet Zack Polanski, the 42-year-old deputy leader of the Green party, in a cafe on the same bridge – Waterloo – where he was first arrested for his part in an Extinction Rebellion protest. “I was leading the charge on the very first day of the very first rally,” he begins. He has a dewy, wide-eyed look and quite a nerdy delivery, very enthusiastic, with no side to it. It takes a bit of getting used to, but once you have, you’re all in. “I did not intend to get arrested. XR ran training on what to do if you get arrested and the ramifications of it, and I didn’t go to any of them, because I just wanted to be on the sidelines and chant. But partly from being an actor, I’ve got a really loud voice.” Someone asked him to lead the chant from the front, which he didn’t want to do. “I always think marginalised communities should be at the front, not me. And the only reason I say that is because there’s a parallel with how I see exemplary leadership – it’s not being out in the front, saying ‘Come this way’, it’s being within and moving together.” Still, he ended up at the front, and saw between one and two hundred police officers. “I remember one pointing at me, and I heard: ‘Get him’.” Before he knew it, he was in handcuffs.

Polanski, who is also chair of the London Assembly Environment Committee, is standing for leader of the Green party, promising a radical new “eco-populism”. When he first announced his intention to stand, the move was portrayed in some quarters as a bid to oust Carla Denyer and Adrian Ramsay, current co-leaders, which he rejects. The Greens elect new co-leaders every two years (Ramsay and Denyer had a three-year term because of the general election; both are now MPs. Denyer has already announced she won’t stand, but Ramsay is running again, in a joint bid alongside fellow new MP Ellie Chowns). Polanski says it’s a perfectly workable model to have a Green MP as a parliamentary party leader and a separate leader of the party at large. “Someone who can lead the party for the country, and be accountable to the membership … I’ve reflected on this because the Green party has never had a solo male leader before, albeit a gay and Jewish one.” He’s bashed these questions around in his head: the tensions between identity and class politics, which I guess could be distilled into “could a man ever lead a radical progressive party?”; the idea of the strong leader (rather than co-leaders) and how much the media needs to see one – and whether it’s against the Green DNA to have one. He’s basically decided that, as valid as all the arguments and counter-arguments are, sod it, he’s going for it.

He emphasises how much he respects Denyer and Ramsay, who, in 2024’s general election, got the best results the party has ever had, with almost two million votes. Nor is his leadership bid a criticism of the local election results, even though all the energy seems to be with Reform, and the Greens are inevitably casualties of that. “It’s mixed,” he says, “it’s a really solid set of results. We’re the only party that has gained in the last eight sets of local elections. In each of those years, almost without failure, the Green vote has been described as a ‘shock’, but how many times are people going to be shocked?

“Reform did really well, you’d be a denier not to admit that, but the asymmetry in how their success has been reported, compared to ours, is really noticeable.” It’s not that he thinks his party is languishing, in other words – just that he wants it to be bolder. By eco-populism, he means go after billionaires, go after water companies, go after corporations. He means retake patriotism. “We should love our country. Loving your community is loving your country.” He means put the climate at the centre of everything – but never forget that these will seem like abstract conversations to people who can’t put food on the table. He wants to lead a party that actively seeks “to improve people’s material conditions, right here and right now”. And the problem with these big, hopeful promises of justice and change is that everyone, from Boris Johnson to Nigel Farage, from Keir Starmer to Ed Davey, makes them. This diet of disappointment has all the same word-ingredients. But the difference with the Greens, Polanski says, is that they mean it, and the answer is better storytelling. “Far too often, the party leads from a policy and data space. Our MPs, who are excellent, are a scientist, an engineer, a renewables expert and a former MEP. We don’t have storytellers. We have such a powerful story to tell.”

Polanski’s own story is that he was born in Salford, his parents divorced when he was quite young, his mum is an actor, his dad works in a DIY shop. “I’m not the son of a tool maker, I’m the son of a tool seller,” he clarifies, very mildly mocking the political cliche of trying to parade working-class credentials. His wasn’t a political family, and it’s taken years to get here, where his parents both vote Green. Much more formative than party politics, in terms of how he handles difference and conflict, is that he “grew up in a very Zionist household, raised to really believe that Israel was the centre of everything and must be defended at all costs. And that’s very different to my politics now, so that’s been a really hard journey, but I always caveat this with nothing is as traumatic as it is to live in Palestine.

“Of all the criticism I’ve received in my career as a politician,” he continues, “the most vicious has come from so-called mainstream Jewish communities. I very much identify as Jewish, I’m very proud to be Jewish, I’m very much involved in Jewish cultures, but I’m certainly not a Zionist, and that’s seen as the ultimate betrayal.”

He went to Stockport Grammar, a private school, on a scholarship. He hated it, got kicked out, and went to a sixth form college. “I remember absolutely loving it and thriving, and suddenly going, ‘Oh, this is what diversity feels like. This is what it feels like when everyone’s not homogeneous.’” Then he went to drama school in Atlanta, Georgia, a pretty random place to go to do a Shakespeare course, which he has no answer to, except that it sounded fun. At this stage, he still felt that “politics was a dirty thing that didn’t really change anything. It wasn’t until I went to America, and saw the inequality, the racism, the homophobia, that I started to wake up.”

Initially, that took a pretty anarchic form. He worked for community projects with homeless people and migrants, “helping people to tell their stories, but also encouraging them to articulate and empower themselves. I did that for years, and I don’t regret the work. But I also kept feeling this deep frustration. You can role-play that someone is overcoming their oppressor, but actually, if the systemic barriers are still there, you’re just setting someone up for failure. People would leave a project feeling so pumped up and ready to go, and they’d see them a year or two later and the problem would still be there.”

He moved back from the US to London in the mid-00s and remembers walking to work because he didn’t have the bus fare, planning his day around when he could get some free lentils from the Hare Krishnas near Russell Square (he’s vegan, by the way – but very insistent that you don’t have to be a vegan to vote Green). “That’s how I was going to make the rent work.” Still, he is very clear that “if the shit hit the fan, I would still have had the bank of mum and dad” and that there is a difference between the temporarily skint and the grindingly poor. “But I’m more interested in the much bigger gap which I see between the super wealthy and the rest. We create divisions between the working class and the middle class, when the real problem is people earning more money in their sleep than you could earn in your life. The real problem is the oligarchy.”

He describes some of the theatre he was making at this time, with the company that later became Punchdrunk – wild, participatory productions in which the audience is invited to alter the course of events. In one performance, an audience member rugby-tackled one of the actors to prevent a murder. In another, Polanski played a leader stewarding the audience into an environmental crisis, and they had to overthrow him. So yes, they were political, because life is, but he was ready for a more formal intervention.

He started by joining the Lib Dems, and standing as a councillor in north London in 2016. “That was for one very clear reason,” he says. “Proportional representation – it’s always been really important to me.” He joined the Greens the following year, was elected a member of the London Assembly in 2021, and deputy leader of the Greens in 2022.

He’s always been an incredibly good communicator, and was a regular on shows like Cross Questions on LBC as soon as he had a presence in his party. His experience as an actor has left Polanski with a genuinely unusual style of political communication – he doesn’t equivocate, his manner is quite urgent and arresting, he never drones, but nor is he embarrassed to say something very simple, even if it sounds schlocky, or boastful. He tells me that the video he launched announcing his leadership bid has been seen 1.4m times. “It’s had hundreds, maybe even thousands of people responding, and I would say 99% of those things are, ‘Is this what hope feels like?’”

Also, distinctively, there are rules he won’t play by. There are all kinds of unspoken norms in current affairs chat. It’s not considered classy to point out that representatives from a rightwing thinktank are most likely speaking for the interests of capital, rather than “ordinary people”, because that would be playing the man not the ball. A Tory might say “multiculturalism has failed”, and they mean “I prefer monoculturalism”, but you’re not allowed to call them racist, because that’s ad hominem, even though, come on, what else are you going to call someone who prefers society to all come from one culture? I remember being struck last year, when three people were shouting at Polanski because he’d used the “r” word. He’s a storyteller, but he’s not a children’s entertainer – sometimes the story is going to be quite challenging.

When he launched his leadership bid, and only the terminally online would know this, a spontaneous community on X sprang into action, saying: “Isn’t he that boob hypnotist?” The community itself included an odd coalition of pro-Russian, anti-trans and pro-Zionist accounts, but the story has a grain of truth. In 2013, Polanski had a hypnotherapy practice, and a Sun journalist went as a client, asked him if he could make her think herself some bigger boobs, and the rest – well, you can read for yourself. To be honest, even if he’d actually set himself up as a breast-enlarger, I’d still have given it a pass – he didn’t know he’d want a career in politics, he was only just 30. If you’ll live on free food in order to make immersive theatre, there are probably other things you’d consider. I only mention all this because there are people who will make it their business that this story dogs Polanski for ever; that’s the world we’re in now. Ordinary people are allowed into democratic politics, until they are difficult or popular – or, heaven forbid, both – and then ways will be found to discredit them; it’s actually a pretty good sign for his campaign that it’s begun.

I’ve heard rumours of imminent Labour defections to the Greens, MPs disaffected by Starmer on Gaza or cosying up to Trump, or cuts to disability allowances, or really, take your pick, finding their way back to the left. Polanski is confident of one but won’t say who. That leap from red to green is a surprising wrench even if you’re a member, or just a voter. “I think it’s the most obvious thing in the world,” Polanski says, “if you align with our values, join us. I want to say to the millions of people who have supported Labour, you’re not leaving the Labour party. The Labour party has left you.”